Multiplex signaling system



Nov. 23 1926. x 1,607,902

R. c. MATHES MULTIPLEX SIGNALING SYSTEM Filed May 1'7, 1921 Small Current.

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UhllTED STATES PATENT OFFICE.

RGBERT C. Iv'IATI-ITES, OF lIEW YORK,-N. Y., ASSIGIIOR T0 VJESTERN ELECTRIC COMPANY,

INCORYEORATED, OF NEW YORK, 31'.

Y., A GOR'PORATZON OF NEW YORK.

IVIULTIPLEX SIGNALING SYSTEM.

Application filed May 17. 1921. Serial No. 470,338.

This invention relates to multiplex signaling systems and more particularly to means foreffecting a balanced condition at the terminal stations associated with a transmis- I sion line;

In multiplex systems heretofore devised it has been proposed toprovide a plurality of channels over which'Morse signals, ordinary voice currents and telegraph and tele- 10 phone signals using carrier currents may be simultaneously transmitted. At the terminal station the line or cable was connected to a net work designed to simulate the impedance characteristics of the line'by parallel inter-- ing paths, while inthe second the selective 30 means was included in the line branch of the interconnecting circuits, that IS between the line and hybrid coil or balanc ng transformer, and a network adapted to simulate the inn pedance of the selective means was included 5 in the network branch of the interconnecting circuits to maintain a balanced'condition at the hybrid coil.

For eiiicient operation, systems of this class demand that the following conditions 40 be met. First, there should be no'interference between channels; second, the energyof one channel must not be dissipated in the other channel connections; and third, a balanced condition must be maintained at each 4- hybrid coil or balancing transformer for all frequencies used in its channels. The first arrangement meets the first and third conditions, and is especially effective as abalancing arrangement because no auxiliary equipment intervenes between the line and network. Moreover, it possesses the additional advantage that, if it is used with a line having a high attenuation which requires that the signal currents transmitted be so large as to require filters of special design and construction, only one filter of special design need be'used for each signal channel.

vHowever, it can meet the second condition only so far as it is possible'to design hybrid coils which are efficient over the frequency range of the whole system. If this cannot be done, serious dissipation of the energy of one channel in the hybrid coils of the other channels may result, since no means is provi'dedlto prevent the flow of signaling currents of all channel frequencies'tlirough the different hybrid coils.

'In the secondarrangement selectivity is assured and dissipation of the energy of the different channels may be prevented by selecting the terminal elements of the filters so that they offer relatively high reactive impedanceto frequencies outside their transmission bands. However, this arrangement requires duplicate filters in the line and network branches of the interconnecting circuits and slight variations in the elements of a multisection filter will produce large im' pedance variations, n their transmission bands, thereby rendering this method somewhat impracticable.

Each of these arrangements, therefore, fails to give the best results, since the first does not prevent dissipation of energy,- and a properly balanced condition at each hybrid coil cannot be obtained with the second.

The present invention is adapted to meet all three conditions outlined above, while retaining theadvantages of the first mentioned arrangement. The primary object ofthis invention is to provide an efficient balancing arrangement in the terminal stations of a multiplex signaling system. Another object is to provide balancing means for the terminal stations of a signal- I ing system adapted for use with a transmission line having high attenuation characteristics. Another object is the provision of an arrangement which permits the signal channels of a multiplex system to be closely spaced in the frequency spectrum without interference or loss of energy between channels. Still another object'is the provision of an arrangement in which the main portion of the frequencydiscriminating devices are external to the interconnecting circuits, while a balanced condition is maintained at the hybrid coils connecting the transmission and receiving paths with these circuits;

. These objects and others, which will ap- 0 Ball pear as the invention is more fully set forth, may be realized by means of the arrangement herein described and shown in the accompanying drawing which illustrates, by way of example, one practical form of the invention which is designed to discriminate )etween ordinary telephone current and carrier currents of higher frequency. Fig. 1 shows the interconnecting circuits arranged in parallel between the line and network, and Fig. 2 shows the conjugate connections for the several channels in series between the line and network.

By this invention advantage is taken of the fact that the impedance characteristics of a filter for frequencies outside of the transmission band for which it is designed, depends almost wholly on the terminal element of the filter. Accordingly the terminal element of the filter and a balancing element of the same impedance characteristic and of equal value are located in the line and network branches of the interconnecting circuits and the main portions of the filters are included in the transmission and receiving paths associated with these circuits. In this manner frequency selection is secured, dissipation of the energy of one channel in the circuit connections for the other channels is ')revented,a balanced condition is easily maintained at each of the hybrid coils, the elements intervening between the line and each hybrid coil are of simple design, and if signal currents of large amplitude are transmitted, but one special filter is required.

In order to illustrate the specific features which characterize this invention it will be hereinafter described in association with a transmission line having a high current attenuation characteristic, such as a submarine cable.

Referring to the drawing, a submarine cable 20, is connected to ground at 21, and by a conductor 3 to the interconnecting circuits l and 5, both of these circuits being connected to the balancing network 12 by the conductors 13. This cable may have a return wire circuit.

The circuit l includes the line windings of the balanced or hybrid coil 14 and the inductances G and 7 each of which has the same impedance value as one series terminal element of a wave filter designed to prevent the flow of high-frequency carrier current through this circuit, while permitting telephone currents to transverse it. The line windings of the hybrid coil 1st are connected to the receiving apparatus for one channel, through the remainder of the wave filter for this channel which is indicated at 10. The bridge winding of the hybrid coil is connected to the transmitter for this channel through a vave filter 11 especially designed to accommodate the current of comparatively large amplitude transmitted to the line.

Circuit has inserted therein the line windings of the balanced coil and the capacity elements 8 and 9 of value equal to one series terminal element of a filter designed to preclude the flow of speech frequency currents through this circuit. The condensers 8 and 9 are of equal impedance value. Another winding of the balanced coil 15 is connected to the receiving circuit of the carrier currentchannel through the remainder of the filter shown at 16 adapted to prevent the flow of telephone currents. The transmitter for this channel is connected to the bridge winding of the coil 15 through a filter 17, which is of special design, but adapted for preventing the flow of speech frequency currents.

Since these filters are adapted to pass a large band of frequencies, a plurality of signal channels each provided with selective means may be associated with them. Again, signal apparatus for other carrier channels may be connected to the cable through appropriate wave filters by means of separate circuits interconnecting the line and network in a manner similar to that described above.

The block sections R and T and R and T are used to schematically represent the receiving and transmitting apparatus for the speech frequency current and carrier waves respectively.

In order to prevent a change in the frequency cut-oft of'the filters 11 and 17 itis of course necessary that the coils included in these networks should be designed to accommodate the maximum current supplied to the cable. Vhile in general the impedance elements included in the line and network branches of the interconnecting circuits will be given the same value as the terminal sections of filters of ordinary design, they may be similar to those included in the filters 11 and 17 should conditions require it.

This method is also applicable to the case where all the hybrid coils are connected in series between the line and balancing network instead of in parallel as is shown in Fig. 1. In this case mid-shunt filter terminal elements will be employed instead of mid-seri es. This is shown in Fig. 2 in which line 22 is connected by the interconnecting circuit 23, which includes the hybrid coils 24 and 25, in series to the balancing network 26. The receiving apparatuses R and R are associated with the line windings of the hybrid coils by means of the windings 24 and 25 through filters 27 of well-known construction, and the transmitters T and T are connected to the bridge windings 24 and 25 of the hybrid coils through specially designed filters 28.

Included in the line and network branches of the interconnecting circuit 23 are midshunt terminal filter elements 6 and 8,

which may correspond, as described above 'with reference to Fig. 1, to those used either in filter 27 orli'lter28; Obviously frequency 7 selection "and prevention of dissipation of the energy of one channel in the hybrid coils of the other channels is eiiected in a manner similar to that described above with reference to the arrangement shown in Fig. 1. From the preceding description, it will be apparent that this invention provides a terminal apparatus which is especially adapted for use in systems including lines having high attenuating properties. As pointed out above, with lines which highly attenuate the current transmitted over them the current supplied from the line to the receivers is of relatively small amplitude and filters of well known design may be used for the incoming currents but the currents supplied by the transmitters to the line are of relatively -large amplitude and filters of special design are required for the outgoing currents. By including the filters 1n thepaths connecting thereceiving and transmitting apparatuses to the line a terminal arrangement having but one specially designed filter for each channel may be used." Again, by inserting a single terminal element of the filter, which serves to make the connecting circuit of high impedance for currents of undesired frequencies, between the lineand conjugate connection for the transmitting and receiving apparatus and a similar eleinent'bet-ween the conjugate connection and the network, the

signal currents of the different channels will be confined to the desired paths and hence will not be dissipated in the hybrid coils connecting the signal apparatus of'tlie other channels to the line. 'FllltllGllHOI'E, this arrangement provides a substantially perfectly balanced condition at the hybrid coils and hence the channels may be closely spaced onthe frequency spectrum without line trouble "practical application of the invention, but it is obvious that it is also applicable to other transmission lines.

While a particular arrangement of elements has been specifically described herein for the purpose of clearly and completely disclosing the invention. itis to be understood that this invention is not to be limited to this disclosure, but covers all modifications coming within the scope of the subjoiiied claims.

What is claimed is: v

1. A multiplex signaling system comprising a transmission circuit, balancing means therefor, a plurality of circuits interconnecting the transmission circuit and balancing means, a plurality of signal channels,

frequency determining means for each signal channel, signal transmitting and receiving apparatus associated with each .interoonnecting circuit, the frequency d-etermining means being inclu-ded,- part in the .intercon necting circuitand-part associated withbotli the transmitting and receiving apparatuses.

2. A multiplex signaling system comprising a groundedtransmission line, balancing means therefor, a plurality of signalingcircuits interconnecting said line and balancing means, signaltransmitting andrreceiving apparatus, conjugately associated, in each of said interconnecting circuits, a frequency determining device for each signale said device and a balancing'm'eans therefor 7 being included in the circuit and the re mainder of said device being associated with both the transmitting and receiving apparatuses.

4. A multiplex ,signalingsystem comprising grounded transmission line, balancing means therefor, a plurality or signal circuits interconnecting said line and balancing means, signal transmitting and receiving apparatus, conjugately associated, in each of said circuits, means includedin each circuit for preventing the dissipation of the signal currents of other signal channels, and means associated with both said apparatuses for effecting frequency selection.

5. in a multiplexsignaling system, comprising a submarine cable, an artificial line for balancing said cable, a plurality of circuits for interconnecting said cable and artificial line, transmitting and receiving-apparatus associated with eachcircuit and selective 11183118,:13311; in -said circuits and part associated with both the transmitting and'receiving apparatuses to provide fre quency discrimination between signal channels. i

6. A multiple signaling system comprising a grounded conductor, means for balancing the conductor, a plurality of balanced signaling circuits interconnecting said conductor and the balancing means, means included in each circuit to prevent dissipation therein of the signal currents of other signal channels and means external to but associated with each circuit and cooperating with the current dissipation preventing means to ef- 3 till channels.

7. A multiplex signaling system comprising a grounded conductor, means for balancing the conductor, a plurality of signaling circuits interconnecting said conductor and balancing means, each including one element of a wave filter having a definite impedance characteristic and balancing means therefor of the same impedance characteristic, the remainder of the filter being external to but associated with said circuit.

8. A multiplex signaling system compri ing a grounded conductor, meansto balance the conductor, a plurality of signaling circuits interconnecting said conductor and balancing means and selective means for providing frequency discrimination between signal channels, part included in and part external to said circuits.

9. A multiplex signaling system comprising a grounded conductor, means to balance the conductor, a plurality of signaling circuits interconnecting said conductor and bal-. ancing means and selective means for providing frequency discrimination between signal channels, one portion of said selective means being included in the interconnecting circuits and the other portions of said selective means for the different channels being external to said circuits.

10. A multiplex signaling system comprising a transmission circuit, means for balancing said circuit, signaling circuits connecting the said transmission circuit and said balancing means, each circuit including two windings of a balanced coil and a pair of elements of equal impedance value and like impedance characteristics one on each side of said windings, and signal apparatus respectively associated with said windings and a third winding of .said coil through impedance elements adapted to cooperate with the previously mentioned impedance elements to constitute frequency selecting means for signal channels.

11. A multiplex signaling system comprising a transmission line, balancing means therefor, a plurality of circuits interconnecting said line and balancing means, conjugate connecting means included in each of said said conjugate connections and between the latter and the balancing means and means selective of the transmitted and received energy respectively included in the transmitting and receiving paths.

18. A signaling system comprising a transmission line, means for balancing said line a plurality of two-way channel terminal apparatuses connected to said line, each. comprising transmitting and receiving apparatuses in conjugate paths, and filtering means for selecting the frequency of each channel having a section located between said line and the connection to said conjugate paths, and other sections located in said conjugate paths, said first mentioned section being adapted to prevent dissipation of the energy of other channels in the respective conjugate connections.

14. A signaling system comprising a transmission line, means for balancing said line, a plurality of two-way channels, connected to said line, the receiving and the transmitting paths in said channels being conjugate, filtering means in each channel for selecting a single frequency, one section of said filter being located between said line and the connection to said conjugate paths, complemental sections included in the receiving and transmitting paths, and an element similar to said firstmentioned section included between said conjugate connection and said line balancing means.

In witness whereof, I hereunto subscribe my name this 13th day of May A. 1)., 1921.

ROBERT c. MATHES. 

